feat(utils): honour __NITRO_JSON_MODE__ flag in JsonParser

Adds three explicit parsing strategies selectable at host build time via
the compile-time constant __NITRO_JSON_MODE__:

- legacy: strict JSON.parse only; clear error suggesting JSON5 mode
- json5 : JSON5.parse only
- auto  : try JSON, fall back to JSON5 (existing behaviour and default
          when the flag is undefined, so older hosts keep working)

URL/MIME hints for .json5 sources are still respected. README updated
with the modes table and a Vite wiring example.

README.md

@@ -15,3 +15,50 @@ yarn
 ```
 yarn add @nitrots/nitro-renderer
 ```
+
+## JSON / JSON5 configuration parser
+
+Every configuration file and gamedata file loaded by the renderer (figuredata,
+furnidata, productdata, effectmap, avatar actions, etc.) goes through
+`@nitrots/utils` → `JsonParser.ts`. The parser supports three modes, selected at
+the **host build time** through the compile-time constant `__NITRO_JSON_MODE__`:
+
+| Mode     | Behaviour                                                                 |
+|----------|---------------------------------------------------------------------------|
+| `legacy` | Strict `JSON.parse` only. Comments / trailing commas raise a clear error. |
+| `json5`  | `JSON5.parse` only. Accepts comments, trailing commas, single quotes.     |
+| `auto`   | Try strict JSON first, fall back to JSON5. Default when the flag is unset.|
+
+URL hints are still honoured: files ending in `.json5` (or served with a
+`application/json5` content-type) always go through JSON5, regardless of mode.
+
+### Wiring the flag into a host
+
+The renderer does **not** ship its own build for the flag — the host application
+(typically [Nitro V3](https://github.com/duckietm/Nitro-V3.git)) defines it via
+its bundler. Example with Vite:
+
+```js
+// vite.config.mjs in the host
+export default defineConfig({
+    define: {
+        __NITRO_JSON_MODE__: JSON.stringify('json5')   // or 'legacy' / 'auto'
+    }
+});
+```
+
+If the constant is not defined the parser falls back to `auto`, which preserves
+the original behaviour of older releases — so existing hosts keep working
+without any change.
+
+### Using the parser directly
+
+```ts
+import { parseConfigJson, fetchConfigJson } from '@nitrots/utils';
+
+const data  = parseConfigJson<MyConfig>(rawText, '/configuration/ui-config.json');
+const data2 = await fetchConfigJson<MyConfig>('/configuration/ui-config.json5');
+```
+
+Errors carry the source URL and, in `legacy` mode, a hint about switching to
+JSON5 — making misconfigurations easy to diagnose in production logs.